Traditional taro monoculture in the swamp forest of Guadeloupe

BOIS ET FORÊTS DES TROPIQUES, 2003, N° 277 (3)
TAR O, FORÊT MARÉCAGEUSE
/ NOTE DE RECHERCHE
taro monoculture in the
swamp forest of Guadeloupe
Traditional
Étienne Saur1-2
Daniel Imbert1
1 Université
des Antilles et de la Guyane,
Laboratoire de biologie et physiologie végétales
Campus de Fouillole
97159 Pointe-à-Pitre Cedex
Guadeloupe (France)
2 Present address:
École nationale des ingénieurs des travaux
agricoles de Bordeaux
Enitab
BP 201
3175 Gradignan Cedex (France)
After a presentation of taro (Colocasia
esculenta) and the native swamp forest of Guadeloupe
dominated by Pterocarpus officinalis, the authors
describe the agrosystem and discuss tree-crop
interactions. They conclude that the agrosystem is
sustainable and profitable in terms of cropping and
forest conservation. This social and agricultural
heritage could enhance the prospects for flooded
agriculture involving water-tolerant nitrogen-fixing
tree associations.
Introduction
Agriculture in the West Indies diverged in two different
directions during the European colonisation period. Export
crops were developed on a large-scale, with few commercially
interesting species such as sugarcane, coffee, cacao and
spices. Food crop production emerged, by necessity influenced by African and later Indian traditions, involving
imported and neotropical species and combining various traditional practices, including those implemented by
Amerindians. The wide range of cultural backgrounds and
environmental situations in the Caribbean islands gave rise to
very diversified agricultural systems.
Swampy areas inhospitable for human activities have,
whenever possible, been widely reclaimed for cattle grazing
and export crop production, or otherwise devoted to resource
extraction (wood, crabs, game). In Guadeloupe, where large
areas of swamp forest have remained fairly undisturbed, the
Creole community has in quite an original way developed
flooded taro monocultures under the forest cover, thus giving
rise to a remarkable agroforestry practice.
Photo 1.
Corms of madère noir taro.
Photo E. Saur.
Taro (Colocasia esculenta)
in Guadeloupe
Taro corms (photo 1) are used in traditional Creole cooking
and consumed boiled like yams, sweet potatoes or bananas.
Unrolled leaves (photo 2) are commonly cooked as a vegetable or served in a local soup called calalu. The local name is
madère (chou de Chine or dachine in Martinique) and seven
cultivars are known to grow in Guadeloupe (Risède, 1984).
Taro was clearly mentioned by Duss (1897), but probably
introduced as a crop in Guadeloupe earlier in the colonial
times. Du Terte (1667) mentioned “fausse racine de Chine”
but did not provide enough details to definitely relate it to
taro. Throughout history, cultivation knowledge seems to have
been perpetuated via family traditions.
During the 20th century, interest in this crop dramatically
decreased and total cultivated areas ranged from 500-600 ha
in the 1950s, 150-250 ha in 1980 (Braux, 1981), to less then
100 ha today (personal data). Administrative authorisations
for taro cultivation under the swamp forest just concerned
74.7 ha in 1999 (Office National des Forêts data).
Taro is grown in three types of farming systems in
Guadeloupe, i.e. monocultures under swamp forest cover,
homegardens and upland monocultures, but monocultures
under swamp forest cover is the system that generates the
highest total crop yield.
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BOIS ET FORÊTS DES TROPIQUES, 2003, N° 277 (3)
SCIENTIFIC NOTE /
TAR O, S WAMP FOREST
Monocultures under swamp forest cover
Flooded taro monocultures under the swamp forest is the
most traditional system encountered in Guadeloupe. Local
farmers consider that the peaty swamp forest soils are good
for taro cropping (terre à madère) when the hydrological conditions are suitable.
Homegardens
Tropical homegardens consist of assemblies of plants, which
may include trees, shrubs, vines and herbaceous plants adjacent to a homestead. These gardens are planted and maintained by members of the household and their products are
intended primarily for household consumption. In Guadeloupe,
this system, which is called jardin créole, averages 0.5 ha in
area and contains up to 40 plant species overall. Taro is planted
annually in shaded environments under the same conditions as
Xanthosoma sagittifolium, another Araceae that is locally called
malanga. Total area and yield are very difficult to evaluate for
the whole island of Guadeloupe, but taro production in homegardens is certainly marginal in terms of quantities produced.
Upland monocultures
Locally, taro monocultures were established after clear-felling
the native forest on the lower slopes of the Basse-Terre volcanic
mountain range. The crop is planted once a year after tillage
and includes fertilisation, weed control and pest management.
Taro cropping units of several ha are collectively managed by
smallholder farmers with intensification objectives. This relatively recent type of farming is presently limited in area, presumably well under 50 ha for the whole island of Guadeloupe.
Photo 3.
Pterocarpus officinalis buttress roots.
Photo E. Saur.
The swamp forest
The swamp forest covers about 2 600 ha of coastal wetlands
in Guadeloupe (Bonhême et al., 1998; Imbert et al., 2000),
mostly along the landward edge of the mangrove forest where
the soil is flooded by freshwater. Pterocarpus officinalis
(photo 3) is the dominant tree species of the forest, forming a
dense, almost evenly flat canopy.
Taro-Pterocarpus association
Cultivation practices
Traditional taro cultivation is conducted in the coastal
swamp forest after partial clearing of the native forest (photos
4 and 5). Long-term clearing operations and control of the forest structure involve hand-cutting (young trees) and burning
(larger ones) (photo 6). A study of this type of agroforestry
system was conducted in Belle-Plaine area (Morne-à-l’Eau).
Mapping of a taro cropping unit highlighted the spatial distribution of a few large Pterocarpus trees that were evenly distributed throughout the plantation (figure 1). On this site,
some young Pterocarpus trees (1-2 m tall) were noted between
taro plants, representing potential future trees. Pterocarpus
tree densities (160 stems/ha) were far lower than those of the
undisturbed forest, which meant that there was only partial
shade at the soil level. On a broader scale, the cultivated forest areas appeared as a mosaic of taro cropping units intermingled with patches of forest cover. Such areas have been
studied along four 5x100 m transects (Imbert et al., 2003).
Generally, the basal area and especially the stem density
(GBH>10 cm) were lower in cultivated forests than in closed
BOIS ET FORÊTS DES TROPIQUES, 2003, N° 277 (3)
TAR O, FORÊT MARÉCAGEUSE
forests, and the number of vascular plants increased due to
the establishment of light-demanding species (table I). The
physical soil properties seemed to remain nearly unchanged
under taro cropping conditions because there was very little
tillage of the top peat layer. Farmers maintain natural drainage
of the forest soil by cleaning the small streams. Investigation
of seven sites over the November to April 2000 period (table II)
revealed that the characteristics of the surface water feeding
these crops spatiotemporally varied to a considerable extent,
but this was compatible with healthy taro development.
The average taro plantation area is small (0.2–2 ha) and
generally cultivated by one person. Nowadays, taro production provides a complementary source of cash income. The
fieldwork is done mainly in the early morning for 2-3 h/day,
when the temperature is reasonably low. Products are sold
daily to retailers or directly through family markets. The farmer
population is ageing (57 years-old, 1980), as youths have
abandoned this activity because of the strenuous work
required in muddy environments.
Two main cultivars (madère or dachine noir and madère or
dachine blanc) are planted, and both are characterised by a
brown colour patch in the middle of the lamina, brown petiole
and dark-brown corms with white flesh. The flesh of madère
noir turns purple-grey after cooking.
Harvest, plantation and weed control are generally completed in single manual operations distributed throughout the
year depending on the market demand (photo 7). However,
these activities are enhanced during the dry season when
accessibility is better. When traditionally conducted, this crop
requires no tillage, fertiliser or organic amendments, and no
pest and disease control chemicals.
Offshoots from the main corm or cormels ensure propagation.
The material is planted at 20-30 cm depth and planting density
ranges from 10 000 to 30 000/ha. The crop cycle lasts for 6-12
months and the annual yield ranges from 5 to 30 t of corms per
hectare. No major pest and disease problems affect swamp forest taro, in contrast to upland taro and Xanthosoma crops.
Photo 2.
Madère noir taro in flooded cropping conditions.
Photo E. Saur.
Photo 4.
Taro-Pterocarpus cropping unit in Guadeloupe with isolated trees.
Photo E. Saur.
Table I.
Mean structural characteristics of closed/cultivated swamp forests
in the Belle-Paine sector (Morne-à-l’Eau, Guadeloupe).
Forest type
Closed forest
Number of trees
(n/ha*)
Basal area
(m2/ha*)
2 400 (1 620)
51 (23)
16 (6)
338 (310)
31 (24)
22 (5)
Cultivated forest
Number of vascular plants
(n/50 m2)
Standard deviations are given in parenthesis
* Stems GBH > 10 cm
Table II.
Chemical characteristics of surface water in taro-Pterocarpus associations.
Temperature
(°C)
pH
Salinity
(mg/l)
Conductivity
(mS)
Minimum
21.2
6.7
0.0
Maximum
35.5
8.3
0.4
Mean
28.2
7.3
0.2
/ NOTE DE RECHERCHE
Dioxygen
(% saturation)
Redox
(mV)
0.01
9
-145
1.23
100
163
0.60
51
25
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TAR O, S WAMP FOREST
Table III.
Mineral contents of Pterocarpus officinalis tissues.
N
(g/kg)
P
(g/kg)
K
(g/kg)
Ca
(g/kg)
Mg
(g/kg)
Fe
(g/kg)
Cu
(mg/kg)
Zn
(mg/kg)
Mn
(mg/kg)
B
(mg/kg)
Na
(g/kg)
Leaf
33.6
1.4
10.9
16.3
Branch
8.5
1.0
3.8
12.7
5.1
0.1
5.4
29.4
116.7
90.7
0.5
1.9
0.2
3.8
8.3
23.5
10.5
1.9
Root
18.6
0.7
5.5
10.5
2.6
10.7
8.0
32.3
43.7
29.1
3.7
Nodule
48.8
3.0
7.2
8.9
4.2
4.1
7.0
27.0
24.1
32.1
4.5
Figure 1.
Mapping of a 0.17 ha taro-Pterocarpus cropping unit
in Belle-Paine (Morne-à-l’Eau, Guadeloupe).
Photo 5.
Taro-Pterocarpus cropping unit in Guadeloupe
with aggregated trees.
Photo E. Saur.
Tree-crop interactions
Empirical practices of Guadeloupian farmers involve maintaining a suitable forest canopy opening so that the taro crops
may benefit from optimum light interception. Competition for
water is clearly not an important factor in this flooded environment. Tree vegetation is deliberately maintained at a certain level to benefit the crops, for many reasons, such as:
▪ to prevent excessive weed development and consequently
reduce hand labour;
▪ to prevent excessive plant transpiration and dryness of the
topsoil and allow cultivation, even during the dry season—taro
is known to be very sensitive to water stress, especially the
root system;
▪ to prevent excessive heating of the soil and surface water so as
to limit the risk of corm rot before harvesting and taro dieback;
▪ to maintain soil fertility by continuous organic matter input.
Fresh organic matter can enhance plant mineral nutrition during the soil mineralisation period when the soil is temporarily
emerged. The high nitrogen content of Pterocarpus tissues
(table III) offers some advantages with respect to nitrogen
input at the stand level;
▪ to prevent hydraulic erosion and soil instability.
Pterocarpus buttresses and root system control hydraulic
erosion of waterlogged peaty soils through mechanical stabilisation.
BOIS ET FORÊTS DES TROPIQUES, 2003, N° 277 (3)
TAR O, FORÊT MARÉCAGEUSE
/ NOTE DE RECHERCHE
References
Discussion
Taro monocultures under native swamp forest cover could
be considered as a traditional agrosystem developed locally in
Guadeloupe, in contrast with other flooded taro cropping systems in other parts of the tropics (Wang, 1983).
Some physiological features of Pterocarpus officinalis and
Colocasia esculenta species are presumably essential to the
success of this wetland crop. Taro exhibits good tolerance to
waterlogging and shade, contrary to several undesirable
weeds and other tropical crops. Pterocarpus trees, which also
tolerate flooding and waterlogging, very likely have a positive
impact on the mineral budget (especially nitrogen) of the
association through efficient symbiotic nitrogen-fixing (Saur
et al., 1998).
This 2-3 century old agrosystem ensures soil conservation
and has a minimal impact on swamp forest vegetation, and
should be regarded as sustainable and profitable in terms of
crop production.
Moreover, we strongly believe that this system should be
preserved as a social and agricultural heritage, and that it
could enhance the prospects for flooded agriculture involving
associations with flood-tolerant nitrogen-fixing trees.
Acknowledgements
We are grateful to P. Julianus, V. Roseau, R. Tournebize (INRA)
and M. Osseux (Chambre d’Agriculture) for agronomical surveys and field assistance.
Photo 6.
Over-cleared Pterocarpus stand with visible hand-cutting
and burning.
Photo E. Saur.
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forêt marécageuse à Pterocarpus officinalis : sa situation en
Guadeloupe. Bois et Forêts des Tropiques, 258: 59-68.
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Guadeloupe. A. Kermarec (ed.), INRA-DGRST, 157-180.
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IMBERT D., BONHÊME I., SAUR E., BOUCHON C., 2000. Floristics and structure of Pterocarpus officinalis swamp forest in
Guadeloupe, Lesser Antilles. J. Trop. Écol., 16: 55-68.
IMBERT D., SAUR E., BONHÊME I., ROSEAU V., 2003. Traditional taro cultivation in the swamp forest of Guadeloupe
(FWI): impact on forest structure and plant biodiversity. Rev.
Écol. – Terre Vie (in press).
RISÈDE J.-M., 1984. Observations préliminaires sur la situation
du madère (Colocasia esculenta) et du malanga (Xanthosoma
sagittifolium) en Guadeloupe. Mémoire de fin d’études ; Institut Supérieur Technique d’outre-mer, 104 p.
SAUR E., BONHÊME I., NYGREN P., IMBERT D., 1998. Nodulation of Pterocarpus officinalis in the swamp forest of Guadeloupe (West-Indies). J. Trop. Écol., 14: 761-770.
WANG J.-K., 1983. Taro. A review of Colocasia esculenta and its
potentials. University of Hawaii Press, 394 p.
Photo 7.
Taro harvest and plantation, a single manual operation.
Photo E. Saur.
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